You might think you don't know Darlene Love. But you're wrong. You've heard her on hits starting in the '60s -- songs like "He's a Rebel," Da Doo Ron Ron," and "Christmas Baby Please Come Home." When you think of that oldies girl group sound, it's her voice you're thinking of.

Love is arguably one of the most important pop musicians of the last century, but few people have heard her name because of a music industry that hid her behind lesser talent. The same goes for Merry Clayton, Lisa Fischer, Tata Vega, and Claudia Lennear -- all backup singers with resumes packed with music's biggest stars (Ray Charles, Tina Turner, the Rolling Stones) whose vocal talents are as unbelievable as the fact that they never became household names.

Twenty Feet From Stardom, the Miami International Film Festival's opening night film, tells the stories of these singers and others, with input from Mick Jagger, Bruce Springsteen, Sting, and Sheryl Crow, among other musicians who've made it into the spotlight. But the real stars of this film are the backup singers -- and after the screening, Darlene Love took the stage to prove that even at 71, she's still got pipes that'll blow your mind.

The women profiled in Twenty Feet From Stardom have only a few things in common: Each grew up singing gospel music in church, and each needs to sing to be fulfilled. Apart from those things, their diverse sounds and histories cover just about the whole of popular music of the past five decades. When she wasn't recording her own songs (which Phil Spector, who owned her contract, repackaged as hits for The Crystals), Love sang with Elvis Presley, Aretha Franklin, and Cher. Claudia Lennear began as one of Ike and Tina Turner's "Ike-ettes," and later toured with Joe Cocker and The Rolling Stones. (She's rumored to have been the inspiration for "Brown Sugar.") Lisa Fischer backed Luther Vandross, Chaka Khan, and Roberta Flack.

But these singers' connections to more famous names only complement the real point of this film: These women can sing with the best of them, literally. Director Morgan Neville lovingly films his subjects singing solo, and their voices are so captivating that you just can't believe you've never noticed them before. Fischer's voice, freestyling smoothly on a jazz riff, feels both light and soulful; when she compares the feeling she has while singing to being a feather floating on a breeze, it makes perfect sense.

But the most impressive vocal moment of the film belongs to Merry Clayton, the woman who sings the famous "Rape, murder, it's just a shot away" line in the Rolling Stones' "Gimme Shelter." The filmmakers unearthed the original recording and stripped away the rest of the music, so we hear only Clayton's solo -- and its stand-alone power damn near blew the top off the Gusman, inspiring last night's audience to spontaneously applaud right in the middle of the film.

If Clayton on film nearly blew the roof off, Love's in-person performance after the screening threatened to burn Gusman to the ground. Love took the stage after the film, looking awed herself by Miami's enthusiastic reaction to her film, then sang the documentary's closing song, "Lean On Me." At 71, her voice sounds like a mature version of the wailing 18-year-old you never knew you knew -- a bit deeper, but just as clear and powerful. At her strongest moments, I felt sure the speakers above my head were going to explode.

If you weren't there last night, you missed one seriously incredible film experience. But there is good news. Twenty Feet From Stardom was picked up at Sundance by Radius-TWC, and is set to open in theaters nationwide June 14.